Granulocyte colony-stimulating factor (G-CSF) stimulates the proliferation and differentiation of neutrophil precursors via interaction with a specific cell surface receptor, the G-CSF receptor (G-CSF-R).
Although the G-CSF-R has been cloned (1) and is functionally active in several different cell types (2), little is known about the mechanism of signal transduction. The G-CSF-R is believed to consist of a single chain that is activated through ligand induced homodimerisation (3) as has been shown for the erythropoietin and growth hormone receptors (EPO-R, GH-R) (4). The G-CSF-R does not contain an intrinsic protein kinase domain (1) although tyrosine kinase activity seems to be required for transduction of the G-CSF signal (5). JAK kinases (6,7) are receptor-associated proteins which are rapidly phosphorylated after receptor activation. In particular, Tyk2 is phosphorylated following interferon .alpha.-receptor (IFN.alpha.-R) activation (8) and JAK2 following the binding of EPO (9), GH (10) and interleukin-3 (IL-3) (11) to their respective receptors.
In work leading up to the present invention, the inventors investigated early signal transduction events resulting from the association of G-CSF with its receptor and the role of JAK1 and JAK2.
In accordance with the present invention, antibodies were prepared to the extracellular domain of G-CSF-R. It has now been surprisingly discovered that G-CSF interaction with G-CSF-R is required for tyrosine phosphorylation of JAK kinases. The antibodies of the present invention now provide for a method of inhibiting G-CSF binding to its receptor and, by consequence, phosphorylation by JAK kinases. The present invention contemplates, therefore, a method for treating G-CSF related disease conditions or JAK1 and JAK2 phosphorylation associated disease conditions which result from G-CSF interaction with its receptor.